Evaluation of Yeast Biomass Production Using Molasses and Supplements

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Addis Ababa University


Three yeast strains of saccharomyces cerevisiae, namely commercial baker’s yeast (BA), an isolate from teff dough (TE) and an isolate from tella(TL) were cultivated in the laboratory by submerged method to determine biomass yield. The biomass of these yeast strains was compared with respect to molasses concentrations(3% w/v,5% w/v,8% w/v and 10% w/v), pH(3.5,4.0,4.5,5.0 and 5.5),growth temperatures ( 250C,300C and 370C), duration of incubation( 24,48,72 and 96 hrs) and the effect of addition of supplements as treatments; T1-(NH4)2SO4 (0.5 % w/v),T2-(NH4)2SO4 (0.5 % w/v) and KH2PO4 (0.3 % w/v),T3-(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 % w/v) and peptone (2% w/v),T4-(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 % w/v),yeast extract(1%w/v) ,MgSO4.7H2O (0.05 % w/v ) and CaCL2.2H2O (0. 004 % w/v ),T5-(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 % w/v), peptone (2%w/v),yeast extract(1%w/v),MgSO4.7H2O (0.05%w/v) and CaCL2.2H2O (0.004% w/v), biotin(0.005%w/v) and calcium panthetonate (0.0001% w/v). The contents of molasses were analyzed before the cultivation process and it was found that the molasses used for this study contains 43.1 % sugar, 0.25% total nitrogen, 1.56 % crude protein, 17.9 % moisture content, 82.1% dry weight and 11.7 % total ash. With respect to molasses concentration, BA isolate showed maximum biomass yield at 5%, 8% and10% concentrations, whereas TE isolates showed the same trend at 5% and 8% concentrations. TL isolate was found to accumulate the maximum yield at 8% molasses concentrations. In all cases, the isolates showed similarity in high biomass accumulation when they were grown at 8% w/v molasses concentration. Concerning the effect of pH on the growth of yeasts, isolate BA was found to be effective at all pH values except pH 5.5; whereas TE isolate was effective at pH 4.0, pH 4.5 and 4.5. Furthermore, isolate BA and isolate TE were also effective at pH 4.5. At pH 3.5 and 5.5, there was a steady decrease in biomass yield by all the isolates. With respect to incubation temperatures, the different isolates displayed biomass yield ranging from 1.27g/l to 3.25g/l. All isolates showed slow growth at 250C, and 370C with subsequent slow increase as the incubation temperatures increased. The highest biomass was observed at 300C by isolates BA (2.98-3.2g/l in 24-72 hrs), TE (2.91-3.1g/l); whereas isolate TLshowed biomass increase of 2.81g/l .Supplementing molasses media with (NH4)2SO4 (0.5% w/v) (Treatment1) increased the biomass of TL (5.6-5.9g/l), TE (5.6-6.2g/l), and BA (6.1-6.4g/l within 24 and 72 hrs. In all cases the maximum biomass was achieved within 48 hrs. When this compared with biomass accumulation on molasses alone, the inclusion of the supplemental nitrogen source showed 1.5-2 fold increase in yeast dry weight by all isolates. Comparing the growth of the isolates on molasses and ammonium sulphate as control the isolates did not show significant difference in biomass with further treatments (T2-T5). The incorporation of all the necessary supplements resulted in maximum biomass production by BA (8.0 g/l), followed by TE (7.5 g/l) and TL (6.5 g/l). In all the biomass propagation processes, the commercial baker’s yeast strain, BA was superior in giving high biomass yield. Further more the leavening action of the two yeast strains, i.e., an isolate from teff dough (TE) and commercial baker’s yeast (BA) was compared at room temperature and 300C. BA was found to be higher than TE both at room temperature and 300C. Key words/phrases/: Baker’s yeast (Saccharomyces cerevisiae), Biomass, Leavening action, Molasses, Supplements



Baker’s Yeast (Saccharomyces cerevisiae), Biomass, Leavening action, Molasses, Supplements